1. Field of the Invention
The disclosed invention generally relates to apparatus for detecting essentially collimated radiation, measuring wavelength values within that radiation, determining the direction to the source of that radiation within an extended field-of-view, and observing the coherence length of sources so as to discriminate between essentially coherent (e.g., laser) and non-coherent radiation, all of which is accomplished simultaneously and in staring fashion (i.e., without scanning).
2. Background Art
The prior art includes a variety of devices for detecting coherent radiation. Examples of such prior art devices are discussed below.
U.S. Pat. No. 3,824,018, issued to Crane, Jr., discloses an unequal path interferometer. The interferometer scans so as to cause a change in the difference in the two optical paths which will modulate the intensity of the recombined coherent radiation by varying interference effects.
U.S. Pat. No. 4,147,424, issued to Foster, et al., discloses a system for detecting the presence of coherent radiation having an interference filter with a pair of partially reflective mirrors, with the spacing between the mirrors being varied sinusoidally to change the transmission wavelength of the mirrors. The output is compared to an established reference signal to produce an identifying indication of the detected radiation.
U.S. Pat. No. 4,170,416 discloses apparatus for detecting the presence of coherent radiation in the presence of incoherent ambient radiation, and for determining the intensity, the wavelength, or the threshold direction of such coherent radiation. The apparatus includes a Fabry Perot etalon having three regions of different thickness.
U.S. Pat. No. 4,183,669, issued to Doyle, and U.S. Pat. No. 4,185,919, issued to Williamson et al., disclose a quadrant detection system using an objective lens and a holographic lens. The holographic lens has lens elements in four quadrants with each quadrant having a focal point corresponding to the position of adjacent photoelectric detectors.
U.S. Pat. No. 3,858,201, issued to Foster, discloses a system for determining a direction from which an illuminating laser beam is received. The system includes a cylindrical optical system for focusing a laser beam as a sharp line image.
U.S. Pat. No. 4,309,108, issued to Siebert, discloses an analyzer for coherent radiation for discriminating wavelength from a single pulse or from a continuous wave radiation and to determine the relative angular position of the source of the radiation. The analyzer includes at least three unequal length path interferometers and detectors for detecting the radiation transmitted through the interferometers.
The foregoing prior art devices are generally complex, relying to a large extent on classical electrooptical techniques and/or the use of scanning.
While the prior art devices exhibit various combinations of features for measuring characteristics of radiation, none, however, has the versatility or all of the particular and extensive features of the disclosed invention combined into a single instrument without the need to scan.